The present invention relates to an inclination sensor which utilizes a liquid member having a free surface. In particular, the invention is concerned with an inclination sensor best suited for a surveying instrument and capable of being constituted in a compact form by disposing a half mirror on an optical path of both the liquid member and a light receiving optical system, as well as a surveying instrument using the inclination sensor.
Heretofore, as a device for detecting inclinations of a surveying instrument there has been used such a bubble tube 10000 as shown in FIG. 9. In the interior of the bubble tube 10000, bubbles 5000 are sealed and electrodes 6000 and 7000 are formed, to measure a capacitance electrically and thereby determine an inclination.
However, since the outer peripheral portion of the bubble tube 10000 is formed of glass, it is weak against impact and a high mechanical accuracy is required, thus giving rise to the problem that the cost is high.
Further, for measuring inclinations in both X- and Y-axis directions, it is necessary to use two bubble tubes 10000 in two-axis directions, thus causing an increase of cost.
Additionally, the bubble tube 10000 is also influenced by changes in ambient temperature and hence it has so far been required to make correction of temperature changes.